This invention relates to a microelectromechanical or nanoelectromechanical resonator array structure, and method of designing, operating, controlling and/or using such an architecture; and more particularly, in one aspect, to a plurality of microelectromechanical or nanoelectromechanical resonators (for example, a plurality of resonators at least one of which includes one or more enhanced nodal points that facilitate substrate anchoring in order to minimize influence of packaging stress and/or energy loss via substrate anchoring) that are mechanically coupled to provide one or more output signals having one or more frequencies.
Generally, high Q microelectromechanical resonators are regarded as a promising choice for integrated single chip frequency references and filter. In this regard, high Q microelectromechanical resonators tend to provide high frequency outputs that are suitable for many high frequency applications requiring compact and/or demanding space constrained designs. However, while the resonator is being scaled smaller, packaging stress, energy loss into the substrate through substrate anchors, reduced signal strength, and/or instability or movement of the center of gravity during oscillation tend to adversely impact the frequency stability as well as “Q” of the resonator.
There are several well-known resonator architectures. For example, one group of conventional resonator architectures employs closed-ended or open-ended tuning fork. For example, with reference to FIG. 1, closed-ended or double-clamped tuning fork resonator 10 includes beams or tines 12a and 12b. The beams 12a and 12b are anchored to substrate 14 via anchors 16a and 16b. The fixed electrodes 18a and 18b are employed to induce a force to beams 12a and 12b to cause the beams to oscillate (in-plane).
The characteristics and response of tuning fork resonator 10 are well known. However, such resonator architectures are often susceptible to changes in mechanical frequency of resonator 10 by inducing strain into resonator beams 12a and 12b as a result of packaging stress. In addition, conventional resonator architectures, like that illustrated in FIG. 1, experience or exhibit energy loss, though the anchors, into the substrate.
Certain architectures and techniques have been described to address Q-limiting loss mechanism of energy loss into the substrate through anchors as well as changes in frequency due to certain stresses. In one embodiment, the beams of the resonator may be “suspended” above the ground plane and sense electrode whereby the vibration mode of the beam is out-of-plane. (See, for example, U.S. Pat. No. 6,249,073). While such architectures may alleviate energy loss through the anchors, resonators that include an out-of-plane vibration mode (i.e., transverse mode) tend to exhibit relatively large parasitic capacitance between drive/sense electrodes and the substrate. Such capacitance may lead to a higher noise floor of the output signal (in certain designs).
Other techniques designed to improve the Q-factor of the resonator have been proposed and include designing the spacing between the vibrating beams so that such beams are closely spaced relative to a wavelength associated with their vibrating frequency. (See, for example, the single-ended or single-clamped resonator of U.S. Pat. No. 6,624,726). The vibrating beams are driven to vibrate one-half of a vibration period out of phase with each other (i.e., to mirror each others motion). While these architectures and techniques to improve the Q of the resonator may suppress acoustic energy leakage, such an architecture remain predisposed to packaging stress, energy loss into the substrate through substrate anchors as well as a “moving” of the center of gravity of the resonator during motion by the vibrating beams of the single-ended or single-clamped resonator.
Further, other resonator architectures have been described to address energy loss through the anchor, for example, a “disk” shaped resonator design. (See, for example, U.S. Patent Application Publication 2004/0207492). Indeed, an array of identical mechanically-coupled disk-shaped resonators has been proposed to decrease motional resistance while improving linearity. (See, for example, U.S. Pat. No. 6,628,177 and “Mechanically Corner-Coupled Square Microresonator Array for Reduced Series Motional Resistance”, Demirci et al., Transducers 2003, pp. 955-958).
There is a need for a resonator array architecture, configuration or structure that overcomes the shortcomings of one, some or all of the conventional architectures, configurations or structures. In this regard, there is a need for improved array of microelectromechanical and/or nanoelectromechanical resonators having improved packaging stress characteristics, reduced and/or minimal energy loss into the substrate though substrate anchors, and/or improved or optimal stability of the center of gravity during oscillation. In this way, the signal to noise of the output signal is increased, the stability and/or linearity of the output frequency of the resonator is enhanced, and/or the “Q” factor of the resonator is relatively high.
Further, there is a need for an improved microelectromechanical resonator array architecture, configuration or structure that includes relatively small motional resistance and good linearity, implements full differential signaling and/or possesses a high immunity to on the input signals and/or the output signals. Moreover, there is a need for an improved method of designing, operating, controlling and/or using such a resonator array that overcomes the shortcomings of one, some or all of the conventional resonator array architectures, configurations or structures.